There are many commercial applications of ion sputtering, in which highly energized particles impinging upon a target cause dislodgement of the target material, either as individual atoms or clusters of atoms, for subsequent deposition as a thin film on a substrate. A variety of techniques are known and practiced for generating and carefully directing the energetic particles, e.g., typically ions of noble gases such as argon, neon or xenon, by carefully applied electrostatic fields either to remove surface impurities from a substrate for cleaning or to sputter off material from a target to deposit the material onto a clean substrate.
U.S. Pat. No. 3,528,387, to Hamilton, discloses an apparatus in which ions of an inert gas are emitted into a deposition vacuum chamber through a small port generally aligned toward the substrate. The ions bombard the substrate to clean its surface prior to deposition, or bombard the substrate during or after a deposition step involving evaporation of the material to be deposited on the substrate.
Apparatus and techniques for producing a thin film deposit on a substrate are shown, for example, in U.S. Pat. No. 4,424,103, to Cole, wherein a target is bombarded obliquely with a linear ion gun. Sputtered target material is sprayed onto moving substrates are to obtain the desired deposits thereon.
A broad ion beam is deflected and focused by means of electrostatic fields in U.S. Pat. No. 4,381,453, to Cuomo et al, and in U.S. Pat. No. 4,250,009, also to Cuomo et al, careful control of such biasing electrostatic fields can be utilized to selectively direct positive or negative ions to a substrate.
Conventional ion guns typically utilize a noble gas to produce a glow discharge from which ions are selectively extracted and accelerated to form an ion beam. Such ion guns, however, have current density limitations which make them unsuitable for employment in certain demanding vacuum processing, cleaning and sputter deposition operations. The use of a magnetron plasma source, wherein a plasma formed between two electrostatic field defining surfaces is ejected energetically toward the target element to be sputtered, is taught in U.S. Pat. No. 4,361,472, to Morrison, Jr. as an alternative ion source.
A need therefore exists for apparatus and techniques that will permit the use of a conventional, inexpensive ion source, e.g., ion gun, for rapid cleaning of substrates or the deposition of thick sputtered deposits thereon in a uniform and smooth distribution. Particularly where sputtered coatings are being considered for use as a cladding on deuterium filled microballoon fuel elements for nuclear energy applications, a smooth and uniform amorphous coating is required to prevent anomalous collapse during implosion. Even where relatively slow deposition rates by known techniques can be tolerated, the slow deposition rates allow residual vacuum system contaminants such as oxygen and carbon to codeposit with the sputtered material in the deposited film. Finally, the controlled effluence of some energetic ions onto the substrate surface during deposition is found to provide deposits with fine crystalline structures that are highly desirable for certain applications. It is therefore desirable to have in a single apparatus the flexibility to control high deposition rates and controlled ion bombardment during deposition, and to obtain sputtered deposition substantially all around a substrate, e.g., a round or spherical object.